$TETMratio

In this program, the definition of TE and TM may not be the same as textbook define. For TE light, it means photon with Ez and Hx, Hy polarized direction. For TM light, it means photon with Hz and Ex, Ey polarized direction.

$TETMratio
Ratio_of_TE_light  (from 0-1) 

If the random number <   Ratio_of_TE_light , it is TE light. 
If the random number >=  Ratio_of_TM_light , it is TM light.

The $TETMratio setting in GUI interface is here
Press Ray Tracing and fill in the field for the Ratio of TE light as needed!